JP2010286354A - Device for estimation of doppler frequency, device for capturing and tracking of positioning signal, positioning device, and method of measuring doppler frequency - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a Doppler frequency estimation device capable of relatively precisely setting a Doppler frequency at an initial point of time of tracking with a simple configuration and low-load processing. <P>SOLUTION: A control unit 35 acquires code correlation data for every prescribed code phase difference over the entire code as primary search processing, and detects a code phase that becomes the maximum code correlation data. Then, the control unit 35 acquires code correlation data for each prescribed code phase difference within a search range set from results of the primary search processing, and detects a code phase that becomes the maximum code correlation data. The control unit 35 calculates a Doppler frequency, namely a frequency error between a carrier frequency for search and an actual carrier frequency from a time interval and the amount of code shift from a code phase that becomes the maximum code correlation data in primary search processing to a code phase that becomes the maximum code correlation data in first secondary search processing. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an apparatus that performs Doppler frequency estimation, code acquisition, code tracking, and carrier tracking of a positioning signal in order to demodulate the positioning signal.

  Conventionally, in a GNSS receiver such as a Galileo receiver, it is necessary to measure a pseudorange or a carrier frequency in order to perform positioning or the like. In order to measure the pseudorange and the carrier frequency, the positioning signal must be captured (searched) and tracked. In particular, in order to measure the pseudorange and Doppler frequency with high accuracy, both code tracking and carrier frequency tracking must be performed.

  However, in such a GNSS receiver, depending on the code acquisition state, in the process of driving and locking the carrier frequency after entering the tracking state, sufficient tracking cannot be performed or the carrier frequency is locked to the wrong carrier frequency. An abnormal tracking phenomenon occurs. Further, along with such an abnormal tracking phenomenon of the carrier frequency, it becomes impossible to execute code tracking with high accuracy by accurately matching the code phase.

  FIG. 6A is a graph showing an example of frequency estimation in C / No = 35 [dB-Hz] in the reception environment in Galileo, from a state where the frequency is shifted by 500 Hz (0 Hz) to an accurate frequency (+500 Hz). It is a graph showing whether or not it can be driven accurately. FIG. 6A shows a case where the “normal” characteristic can accurately drive the frequency, and a case where the “No1” to “No6” characteristics are frequency estimation errors.

  FIG. 6B is a graph showing C / N [dB-Hz] obtained from the code correlation result with the characteristics of “normal” and “No1” to “No6” in the case of FIG. It is.

  As shown in FIGS. 6A and 6B, when a complex code such as Galileo is used in an environment where the received signal level is low such as C / No = 35 [dB-Hz]. If the initial frequency is shifted by 500 Hz, it is almost impossible to perform high-accuracy code tracking by locking to an accurate frequency.

  This is because the tracking processing unit that tracks the code phase and the carrier frequency at the same time feeds back the tracking result of the carrier frequency to the tracking processing of the code phase. This is because even if the code phase is driven using a non-carrier frequency, if tracking is not started in a state where the initial code phase almost coincides with the true code phase, the code phase shifts from the true code phase. For example, in the above-described Galileo receiver under the reception environment of C / No = 35 [dB-Hz], when the initial frequency is shifted by 500 Hz, an accurate code can be obtained unless the initial code phase error is about 0.13 chip or less. Phase and carrier frequency tracking cannot be realized.

  As a method of solving such a problem, after performing the search process, the code single tracking process is performed, and after confirming that the code phase difference has become sufficiently small, a predetermined time length (for example, 1 second) is set. A method is considered in which the code phase difference is observed, the initial value of the carrier frequency is estimated from the least square value of the code phase difference, and the carrier frequency is tracked from the initial value. Furthermore, Patent Document 1 uses a plurality of channels for one positioning satellite (positioning signal), performs peak search, sidelobe check corresponding to the peak, and carrier frequency confirmation of the peak value, thereby ensuring accurate A method of narrowing down the carrier frequency is also considered.

JP 2004-12378 A

  However, in the case of the method using the least square method described above, one channel may be allocated to one positioning satellite (positioning signal). However, since the least square method is used, the calculation processing amount increases and the processing load increases. Becomes larger. Moreover, since the method as shown in Patent Document 1 requires two channels for one positioning satellite (positioning signal), a lot of resources are required.

  In view of these problems, an object of the present invention is to realize a Doppler frequency estimation device and a Doppler frequency measurement method that accurately estimate a Doppler frequency included in a carrier frequency with a simple configuration and low-load processing. It is in. Another object is to realize a positioning signal acquisition device and a positioning device that can set the carrier frequency at the initial tracking point with high accuracy.

  The present invention relates to a Doppler frequency estimation apparatus for estimating a Doppler frequency of a signal whose spectrum is spread by a predetermined code. The Doppler frequency estimation apparatus includes a correlation unit, a control unit, and an estimation unit. The correlator performs correlation processing between the spread spectrum signal and the code-based replica code. The control unit performs a search process for calculating a correlation level for each predetermined code phase over a predetermined search range at a preset estimation carrier frequency and detecting a code phase having a maximum correlation level with respect to the correlation unit. Let it run. The estimation unit calculates the frequency error of the estimated carrier frequency based on the code shift amount between the code phases that is the maximum correlation level detected in the two search processes and the detection timing interval of the code phase that is the maximum correlation level. The Doppler frequency is estimated by calculation.

  Further, the control unit of the Doppler frequency estimation apparatus according to the present invention performs a primary search process for performing a search process using the entire code as a search range, and performs a search process in a search range narrower than the search range of the primary search process 2 The next search process is executed on the correlation unit. The estimation unit estimates the Doppler frequency based on the amount of code shift between the code phases of the maximum correlation level obtained by the primary search process and the secondary search process and the detection timing interval of the code phase that becomes the maximum correlation level. .

  Further, the code phase of the maximum correlation level obtained by the immediately preceding search process of the Doppler frequency estimating apparatus of the present invention is set as the center code phase, and the correlation level for each code phase is determined in a predetermined search range narrower than the search range of the immediately preceding search process. The secondary search process for obtaining and detecting the code phase that provides the maximum correlation level is executed by the correlator a plurality of times. The estimation unit includes a code shift amount between code phases of the maximum correlation level obtained by two search processes of the primary search process and at least one secondary search process, and a code having the maximum correlation level. The Doppler frequency is estimated based on the phase detection timing interval.

  The present invention also relates to a Doppler frequency estimation method for estimating a Doppler frequency of a signal whose spectrum is spread by a predetermined code. In this Doppler frequency estimation method, a maximum correlation is obtained by calculating a correlation level between a spread spectrum signal and a code-based replica code for each predetermined code phase over a predetermined search range at a preset estimation carrier frequency. A search process for detecting a code phase to be a level is executed a plurality of times. By calculating the frequency error of the estimated carrier frequency based on the code shift amount between the code phases that becomes the maximum correlation level detected in the two search processes and the detection timing interval of the code phase that becomes the maximum correlation level. Estimate the Doppler frequency.

  According to the Doppler frequency estimation method of the present invention, the search processing includes a primary search process in which the entire code is used as a search range, and a search process in a search range narrower than the search range of the primary search process. Secondary search processing. The Doppler frequency is estimated based on the amount of code shift between the code phases of the maximum correlation level obtained by the primary search process and the secondary search process and the detection timing interval of the code phase at the maximum correlation level.

  In the Doppler frequency estimation method according to the present invention, the search process uses the code phase of the maximum correlation level obtained by the immediately preceding search process as the center code phase, and for each code phase in a predetermined search range narrower than the search range of the immediately preceding search process. The secondary search process is acquired a plurality of times to acquire the correlation level and detect the code phase that becomes the maximum correlation level. Then, the code shift amount between the code phases of the maximum correlation level obtained by the two search processes of the primary search process and at least one secondary search process, and the code phase of the maximum correlation level The Doppler frequency is estimated based on the detection timing interval.

  In these configurations and estimation methods, the code phase shift amount includes an error (corresponding to the Doppler frequency) between the estimation carrier frequency and the actual carrier frequency set during the search process, the time required for the code phase shift, It depends on that you depend on. Using this relationship, in multiple consecutive search processes in acquisition mode, the code phase interval that is the maximum correlation level in each search process, that is, the amount of code phase shift, and the code phase shift By detecting the time, a frequency error corresponding to the Doppler frequency can be calculated.

  Further, the control unit of the Doppler frequency estimation apparatus according to the present invention determines the search range based on the time from the code phase of the maximum correlation level by the immediately preceding search process to the last code phase of the immediately preceding search process during the secondary search process. To set.

  In this configuration, if there is a frequency error, the code phase is shifted according to the magnitude of the frequency error from the timing of the code phase at which the maximum correlation level is obtained in the immediately preceding search processing to the timing of the start of the current search processing. To do. If the frequency error is constant, the amount of code phase shift is the time interval between the timing of the code phase at which the maximum correlation level is reached and the timing of the last code phase of the search process in which the code phase at the maximum correlation level was obtained Determined by. Therefore, if the code search range is set to be within the predetermined Doppler frequency range based on this time interval, the code phase having the same maximum correlation level as the previous search within the Doppler frequency range based on this time interval Can be reliably detected. Thus, the frequency error can be calculated reliably by detecting the code phase that continuously has the maximum correlation level.

  In addition, the control unit of the Doppler frequency estimation device according to the present invention may calculate the calculated Doppler frequency when the Doppler frequency is out of the frequency range corresponding to the search range set in the secondary search process used for calculating the Doppler frequency. Correct to a value within the frequency range.

  Further, the control unit of the Doppler frequency estimation device of the present invention, when the frequency calculation error range of the Doppler frequency is out of the frequency range corresponding to the search range set in the secondary search process used for calculating the Doppler frequency, The Doppler frequency is corrected so that the frequency calculation error range is within the frequency range.

  In these configurations, since the calculated Doppler frequency includes a predetermined calculation error, there is a possibility that the calculated frequency range is out of the frequency range used for setting the search range. ing. In these cases, it can be identified that at least a frequency error exists. Therefore, when the Doppler frequency itself deviates from the set frequency range, the Doppler frequency is corrected so as to be within the frequency range. In addition, when the calculation error range of the Doppler frequency is at least partially out of the frequency range corresponding to the search range, the Doppler frequency is corrected so that the entire calculation error range falls within the frequency range corresponding to the search range. . By performing such correction, it is possible to prevent the Doppler frequency from becoming a value that is impossible in calculation.

  In addition, the control unit of the Doppler frequency estimation apparatus according to the present invention detects only a code phase having a maximum correlation level equal to or higher than a preset threshold value.

  In this configuration, the specific processing of detecting the code phase having the maximum correlation level described above is shown, and only the maximum correlation level exceeding a preset threshold is set as a detection target. Thereby, erroneous detection due to noise can be suppressed.

  The control unit of the Doppler frequency estimation apparatus according to the present invention calculates the frequency error using the center code phase of the primary search and the center code phase of the secondary search immediately after the primary search.

  This configuration also shows a specific process, and a primary search in a plurality of search processes and a secondary search immediately thereafter (the first secondary search when there are a plurality of secondary searches). And are used. In the above-described search processing executed in a plurality of secondary searches that are continued from the primary search, the search range is gradually narrowed, and therefore the search time is longer for the first search.

  Here, the calculation of the frequency error corresponding to the Doppler frequency is a positioning signal acquisition and tracking device and a positioning device, which will be described later, using the Doppler frequency. In the case of a device for Galileo, the following (Equation 1) is used. Done. In (Expression 1), Derr is the frequency error, Cmove is the code shift amount between the code phase of the maximum correlation level of the immediately preceding search process and the code phase of the maximum correlation level of the current search process, and tb is the immediately preceding search process. , The time length from the code phase timing of the maximum correlation level to the timing of the last code phase of the immediately preceding search process, tn from the start timing of the current search process to the code phase timing of the maximum correlation level of the current search process Is the length of time.

Derr = −1540 × Cmove / (tb + tn) − (Formula 1)
Therefore, the resolution of the Doppler frequency can be improved as the time length of the two search processes is longer and the code phase shift amount between them is larger.

  FIG. 7 is a diagram showing the relationship between the time length (tb + tn) obtained from the two search processes and the maximum error of the calculated Doppler frequency, that is, the resolution. As shown in FIG. 7, the longer the time length (tb + tn), the smaller the maximum error and the higher the resolution.

  For this reason, if the primary search and the secondary search immediately thereafter are used, the Doppler frequency can be calculated with a relatively high resolution compared to the case of using a combination of other searches. In particular, in the situation where C / No is low, the above-described search process takes time, so that the resolution can be further increased. Thus, in a situation where C / No is low, the Doppler frequency can be estimated with high accuracy, contrary to the conventional case. As a result, since the positioning device can set a highly accurate initial carrier frequency even in a situation where the reception environment is bad, reliable and highly accurate code tracking and carrier frequency tracking can be realized.

  The present invention also relates to a positioning signal acquisition and tracking device having the above-described Doppler frequency estimation device. Then, the control unit is a code acquisition mode for performing a search process that uses a process for capturing a code of a positioning signal that is a spread spectrum signal for estimation of a Doppler frequency, a code tracking mode for tracking a code of a positioning signal, A carrier tracking mode for tracking the carrier frequency of the positioning signal is set, and the code acquisition mode is switched to the code tracking mode and the carrier tracking mode based on the code acquisition result in the code acquisition mode.

  Furthermore, when the new search range in the code acquisition mode is less than a predetermined code chip, the control unit switches from the code acquisition mode to the code tracking mode and the carrier tracking mode. In the code tracking mode, the control unit starts code tracking using the code phase detected by the search process when switching from the code capturing mode to the code tracking mode. Along with this processing, in the carrier tracking mode, the control unit starts tracking the carrier frequency with the initial carrier frequency based on the Doppler frequency estimated by the estimation unit as an initial value.

  In this configuration, since the Doppler frequency estimation device described above is included, a reliable and relatively highly accurate Doppler frequency can be obtained. Thus, an initial carrier frequency for carrier tracking is calculated from the Doppler frequency, and a carrier tracking unit is obtained. Can be given to. As a result, the carrier tracking unit can estimate the carrier frequency with relatively high accuracy from the initial state, and enables reliable and accurate carrier tracking. Along with this, particularly in the case of performing the concatenated code carrier tracking loop processing, the carrier tracking result is fed back to the tracking of the code phase, so that reliable and accurate code tracking is also possible.

  In addition, the positioning device of the present invention includes the positioning signal acquisition and tracking device described above, and also includes a demodulation unit, a navigation message acquisition unit, and a positioning unit. The demodulation unit calculates the pseudo distance based on the code phase difference in the code tracking mode and the carrier frequency in the carrier tracking mode. The navigation message acquisition unit acquires a navigation message from the positioning signal demodulated by the demodulation unit. The positioning unit performs a positioning calculation using the pseudo distance and the navigation message.

  In this configuration, as described above, since the carrier frequency and the code phase can be tracked with high accuracy, it is possible to perform highly accurate positioning.

  According to the present invention, the Doppler frequency included in the carrier frequency of the captured spread spectrum signal can be set with high accuracy. Thereby, since the initial carrier frequency at the time of switching from the acquisition mode to the tracking mode can be set with high accuracy for the positioning signal which is a spread spectrum signal, accurate code phase tracking and carrier frequency tracking can be reliably executed. At this time, the code phase is detected by a normal search process, and the calculation of the Doppler frequency can be performed by a simple calculation process. Therefore, it is not necessary to perform a complicated circuit configuration or a complicated calculation process. Accurate code phase tracking and carrier frequency tracking can be reliably started with low-load processing.

It is a block diagram which shows schematic structure of the positioning apparatus containing the demodulation part corresponded to the positioning signal acquisition tracking apparatus which concerns on embodiment of this invention. It is a block diagram which shows the main structures of the demodulation part 13 shown in FIG. It is a flowchart which shows the calculation flow of a Doppler frequency. It is a figure which shows the calculation principle of a Doppler frequency. It is a figure which shows the concept of each correction process of frequency error Derr. It is a graph which shows the example of the frequency estimation in C / No = 35 [dB-Hz] of reception environment in Galileo. It is a figure which shows the relationship between the time length (tb + tn) obtained from two search processes, and the maximum error of the calculated Doppler frequency, ie, resolution | decomposability.

  Configurations of a positioning signal acquisition device, a positioning signal acquisition tracking device, and a positioning device according to an embodiment of the present invention will be described with reference to the drawings. In the following description, the case of Galileo will be described as an example. However, the following configuration is also applied to a positioning signal acquisition device, a positioning signal acquisition tracking device, and a positioning device in other systems of GNSS such as GPS. can do.

  FIG. 1 is a block diagram showing a schematic configuration of a positioning device including a demodulator corresponding to the positioning signal acquisition and tracking device according to the present embodiment.

  The positioning device includes a positioning signal receiving antenna 11, a down converter 12, a demodulating unit 13 including a positioning signal capturing device of the present invention and a positioning signal capturing and tracking device having the positioning signal capturing device, a navigation message acquiring unit 14, and a positioning unit 15. The positioning signal receiving antenna 11 receives a positioning radio signal transmitted from the Galileo satellite, and outputs a positioning signal obtained by converting the electrical signal to the down converter 12. The positioning signal is a signal obtained by spectrum-spreading a carrier wave having a predetermined frequency using a code set for each positioning satellite and a navigation message. The down-converter 12 down-converts the frequency of the positioning signal to generate an intermediate frequency signal (hereinafter referred to as “IF signal”) having a predetermined frequency, and supplies it to the demodulator 13.

  The demodulator 13 performs carrier correlation and code correlation on the spread spectrum IF signal, and performs despreading by integrating the signals after the correlation processing over a predetermined time length. Here, if the carrier correlation and the code correlation are performed with high accuracy, only the navigation message is superimposed on the despread signal.

  In the acquisition mode, the demodulator 13 performs a search process for roughly acquiring the code phase using a preset search carrier frequency. This search process is executed a plurality of times while gradually narrowing the search range based on the previous search result, and when the new search range falls within a predetermined chip range (for example, 1 chip), the mode shifts from the capture mode to the tracking mode. During this acquisition mode, the demodulator 13 estimates and calculates the Doppler frequency by a method described later, and sets the initial carrier frequency during carrier tracking using the estimated and calculated Doppler frequency.

  After performing the above-described code phase search process, the demodulator 13 performs a concatenated code carrier tracking loop process based on the code phase and the initial carrier frequency that are search results. Here, the simple concatenated code / carrier tracking loop process corresponds to the phase-synchronized DLL process. When the code tracking unit 33 performs code phase tracking and the carrier tracking unit 34 performs carrier frequency tracking. In addition, this is a tracking processing method in which the carrier frequency calculated by the carrier tracking unit 34 is fed back to the code tracking unit 33 and used for the code tracking process.

  When the steady tracking is successful, the demodulator 13 despreads the IF signal with the obtained code phase and carrier frequency information and gives it to the navigation message acquisition unit 14, and the pseudo distance is obtained from the obtained code phase and carrier frequency information. Are calculated and given to the positioning unit 15.

  The navigation message acquisition unit 14 acquires a navigation message based on the despread signal on which the navigation message from the demodulation unit 13 is superimposed, and provides the navigation unit 15 with the navigation message.

  The positioning unit 15 performs a positioning calculation based on the navigation message from the navigation message acquisition unit 14, the pseudo distance from the demodulation unit 13, carrier frequency information, and the like, and calculates the position of the positioning device.

Next, the configuration of the demodulation unit 13 will be specifically described with reference to FIGS. 2, 3, and 4.
FIG. 2 is a block diagram showing a main configuration of the demodulator 13 shown in FIG. FIG. 3 is a flowchart showing a calculation flow of the Doppler frequency. FIG. 4 is a diagram illustrating the principle of calculating the Doppler frequency.

  The demodulating unit 13 includes a correlator 31, an integrating unit 32, a code tracking unit 33, a carrier tracking unit 34, a control unit 35, a pseudo distance calculation unit 36, and an estimation unit 37.

  The correlator 31 performs correlation processing on the IF signal as described above. The correlator 31 includes a carrier correlator, a code correlator, a replica carrier frequency signal generation unit, and a replica code signal generation unit.

  In the acquisition mode, the correlator 31 generates a replica carrier frequency signal based on the search carrier frequency information set in advance by the control unit 35. Further, the correlator 31 generates a replica code signal having a predetermined code phase based on the code information from the code NCO 330 of the code tracking unit 33 controlled by the control unit 35, and performs correlation using the code correlator. This search process is repeatedly performed while changing the center code phase and search range of the search until a switching control signal is input from the control unit 35. When the correlator 31 receives the switching control signal from the control unit 35, the correlator 31 switches to the correlation processing for tracking.

  In the tracking mode, the correlator 31 generates a replica code signal based on the code information output from the code tracking unit 33 based on the concatenated code carrier tracking loop process, and the carrier frequency output from the carrier tracking unit 34 A replica carrier frequency signal is generated based on the information. The carrier correlator of the correlator 31 performs carrier correlation processing between the IF signal and the replica carrier frequency signal, and the code correlator performs code correlation processing between the IF signal after carrier correlation and the replica code signal.

  As described above, the integrating unit 32 applies the signal after the correlation processing in the tracking mode to a predetermined time length, for example, 1 [msec. ] To generate a despread signal. The despread signal is given to the navigation message acquisition unit 14 and also to the code tracking unit 33 and the carrier tracking unit 34.

  Although specific processing will be described later, the control unit 35 roughly sets a primary search process and at least one secondary search process at a preset search carrier frequency in the acquisition mode. In the primary search process, the control unit 35 controls the correlator 31 so that the code correlation process is performed for each predetermined code phase difference over the entire code used in the positioning signal. In the secondary search process, the control unit 35 sets the center code phase and search range of the current search process for the correlator 31 based on the correlation data obtained by the search process immediately before being output from the correlator 31. To do. In the above-described primary search process and secondary search process, the control unit 35 controls the code NCO 330 to generate code phase information corresponding to the search range and the center code phase, so that the correlator 31 is controlled. Set the center code phase and search range of the search process.

  The control unit 35 detects the switching timing from the acquisition mode to the tracking mode based on the search result output from the correlator 31 and outputs a switching control signal to the correlator 31.

  The estimation unit 37 acquires the code phase that is the maximum correlation level and the detection timing of the code phase that is the maximum correlation level in a plurality of search processes output from the correlator 31 during the acquisition mode, and these code phases A frequency error Derr corresponding to the Doppler frequency is calculated from the difference between the two and the detection timing interval. When the estimation unit 37 acquires the timing of switching from the control unit 35 to the tracking mode, the estimation unit 37 gives the Doppler frequency calculated at the timing to the control unit 35.

  The control unit 35 sets an initial carrier frequency using the Doppler frequency and the search carrier frequency from the estimation unit 35, and gives the carrier tracking unit 34 with the switching timing from the acquisition mode to the tracking mode.

  The code tracking unit 33 includes a code NCO 330, a code phase difference detection unit 331, a first unit conversion unit 332, a first amplification unit 333, a second amplification unit 334, an integration unit 335, an adder 336, and a second unit conversion unit 337. Prepare. The code tracking unit 33 does not operate in the capture mode except for the code NCO 330, and operates as a whole after switching to the tracking mode.

  The code phase difference detection unit 331 detects the code phase difference included in the despread signal, that is, the code phase difference between the replica code signal generated based on the code information of the code NCO 330 and the IF signal, and the first unit This is given to the conversion unit 332. The first unit conversion unit 332 converts the code phase difference based on the code chip unit into a code phase difference in time unit, and outputs the code phase difference to the first amplification unit 333, the second amplification unit 334, and the frequency estimation unit 339. To do.

  The first amplifying unit 333 outputs a baseband component of the code phase difference, and the second amplifying unit 334 is set to gain so as to output a code Doppler component with respect to the code phase. The code phase difference obtained from the first amplifying unit 333 is input to the adder 336. On the other hand, the code phase difference obtained from the second amplifying unit 334 is input to the integrating unit 335.

  The accumulating unit 335 sequentially accumulates the code phase differences obtained from the second amplifying unit 334. Here, the code phase difference accumulated in the accumulating unit 335 is a code Doppler component generated by the movement of the positioning satellite or the like. Therefore, by integrating these, the code Doppler component is integrated, and as a result, processing corresponding to integrating the amount of change in the carrier frequency that sequentially changes can be performed. . The integrated value of the code phase difference is given to the fourth unit conversion unit 343 of the carrier tracking unit 34.

  The adder 336 transmits the carrier frequency information (refer to the description section of the carrier tracking section 34 below) converted to the time unit obtained from the third unit conversion section 342 of the carrier tracking section 34 and the first amplification section 333. The code phase difference of the baseband component is added and output to the second unit converter 337.

  The second unit conversion unit 337 converts the code phase difference in units of time into code phase differences in units of code chips and provides the code NCO 330 with the code phase difference.

  In the tracking mode, the code NCO 330 generates code phase information for generating a replica code signal at the next timing based on the given code phase difference, and outputs the code phase information to the correlator 31. The code NCO 330 generates code phase information based on the code control given from the control unit 35 as described above in the acquisition mode.

  The carrier tracking unit 34 includes a carrier tracking execution unit 341, a third unit conversion unit 342, and a fourth unit conversion unit 343.

  The fourth unit conversion unit 343 converts the integrated value of the code phase difference from the integration unit 335 of the code tracking unit 33 from a time unit to a frequency unit, and provides the carrier tracking execution unit 341 with it.

  The carrier tracking execution unit 341 has a known configuration such as a carrier NCO and a carrier difference detection unit, performs various processes related to carrier tracking, and outputs carrier frequency information to the correlator 31. The carrier tracking execution unit 341 does not operate in the acquisition mode and starts carrier tracking from the time when the mode is switched to the tracking mode.

  At the start of carrier tracking, the carrier tracking execution unit 341 starts carrier tracking according to the initial carrier frequency given from the control unit 35. Thereby, since carrier tracking can be started with a relatively high accuracy carrier frequency from the initial state, carrier tracking can be performed reliably and with high accuracy.

  Then, the carrier tracking execution unit 341 outputs the calculated carrier frequency information to the correlator 31, the third unit conversion unit 342, and the positioning unit 15.

  The third unit conversion unit 342 converts the carrier frequency information obtained by the carrier tracking execution unit 341 into a change rate of time, that is, a time unit, and provides the same to the adder 336 of the code tracking unit 33. At this time, the third unit conversion unit 342 performs conversion at a conversion rate according to the code to be tracked. With such a configuration, a concatenated code carrier tracking loop including the code tracking unit 33, the carrier tracking unit 34, the correlator 31, and the accumulating unit 32 is configured, and the code phase and the carrier frequency are tracked in parallel. It is possible to track with high accuracy from the initial state.

  The pseudo distance calculation unit 36 calculates a pseudo distance based on the code phase difference from the code tracking unit 33, the carrier frequency information of the carrier tracking unit 34, and the like, and provides the pseudo distance to the positioning unit 15.

  Next, with reference to FIG. 3 and FIG. 4, a Doppler frequency calculation method and an initial carrier frequency calculation method executed in the acquisition mode (search process), and a detection method of the switching timing from the acquisition mode to the tracking mode will be described. This will be described in detail. In the following description, the flowchart shown in FIG. 3 will be mainly described.

  First, the control unit 35 sets a search carrier frequency fs consisting of a preset fixed value to the correlator 31 (S101). Here, it is assumed that the search carrier frequency fs does not include a Doppler frequency. That is, the Doppler frequency is set to “0”.

  The correlator 31 performs code correlation processing at the given search carrier frequency fs to obtain code correlation data (S102). At this time, the control unit 35 first sets, as a primary search, the entire code range of the code used in the target positioning signal as the search range, and obtains code correlation data for each code phase difference of 0.25 chip. Obtain (see primary search in FIG. 4).

  The control unit 35 acquires the maximum value from all the code correlation data in the search range, and ends the primary search process if the maximum code correlation data is equal to or greater than a preset primary search detection threshold. The process proceeds to the secondary search process (S103: Yes). By setting the detection threshold in this way, the peak level of correlation data due to such noise is generally the peak level of true code correlation data even when the maximum code correlation data is obtained with an incorrect code phase due to noise or the like. Since it is not higher than the level, detection of an incorrect code phase can be suppressed.

  The control unit 35 stores the code phase that is the maximum code correlation data of the primary search process, and performs the last code correlation process of the primary search process from the code phase that is the maximum code correlation data The time interval t1 until is stored. In addition, the control unit 35 detects and stores the code phase shift amount Cmove1 from the code phase serving as the maximum code correlation data to the code phase for performing the last code correlation process (see the primary search in FIG. 4).

  On the other hand, if the maximum code correlation data does not reach the primary search detection threshold, the control unit 35 sets the search carrier frequency fs to a predetermined frequency (for example, the estimated error range of the Doppler frequency is ± 500 [Hz]). The above-described primary search process is performed again with the entire code as the search range (S103: No → S101).

The control unit 35 sets the code phase, which is the maximum code correlation data obtained in the primary search process, as the center code phase of the first secondary search process, and performs the primary search based on the time interval t1. Even if the actual carrier frequency is deviated in the predetermined frequency range with respect to the search carrier frequency fs set in the processing, the code phase that becomes the maximum code correlation data is obtained in the current (first) secondary search processing. A search range is set so that it can be detected (S104). Specifically, in the Galileo system, assuming an estimated deviation of Doppler frequency of ± 500 [Hz] (estimated deviation of carrier frequency), as described in the first secondary search in FIG. From the relational expression of the code phase shift due to Doppler shift, the search range of the first secondary search process is
(1000 [Hz] × t 1/1540) [chip] − (Formula 1)
Set with.

  When the control unit 35 sets the center code phase and the search range of the first secondary search process, the correlator 31 executes the code correlation process at the same search carrier frequency fs as the immediately preceding primary search process. Similarly to the above-described primary search process, code correlation data is acquired for each code phase difference of 0.25 [chip] (S105).

  The control unit 35 acquires the maximum value from all the code correlation data in the current search range, and if the maximum code correlation data is equal to or greater than a preset first secondary search detection threshold, the first time. The secondary search process is terminated (S106: Yes).

  At this time, the control unit 35 stores the code phase that is the maximum code correlation data, and the maximum code correlation data from the code phase that performs the first code correlation process of the current (first) secondary search process. The time interval t2 until the code phase becomes is stored. In addition, the control unit 35 detects the code phase shift amount Cmove2 from the code phase that performs the first code correlation process of the current (first) secondary search process to the code phase that becomes the maximum code correlation data. Remember. Further, the control unit 35 stores a time interval t3 from the code phase that is the maximum code correlation data of the current (first) secondary search process to the code phase that performs the last code correlation process (FIG. 4). (Refer to the 1st secondary search).

  On the other hand, if the maximum code correlation data does not reach the first secondary search detection threshold, the control unit 35 shifts the search carrier frequency fs by a predetermined frequency as in the case of the primary search process, and again Then, the above-described primary search process in which the entire code is set as the search range is performed (S106: No → S101).

  Next, when the control unit 35 detects that the current search process is the first secondary search process (S107: Yes), the estimation unit 37 has already detected and stored the above-described time intervals t1 and t2. And the code shift amounts Cmove1 and Cmove2 are used to calculate a frequency error Derr corresponding to the Doppler frequency from the following equation, as shown in the secondary search process of FIG.

  First, the estimation unit 37 calculates the code shift amount Cmove from the code phase that is the maximum code correlation data in the primary search process to the code phase that is the maximum code correlation data in the first secondary search process. Calculate using Cmove = Cmove1 + Cmove2.

Next, the estimation unit 37 calculates the frequency error Derr from the relational expression of the code phase shift caused by the Doppler shift.
Derr = −1540 × Cmove / (t1 + t2) − (Formula 2)
Calculate using.

  Further, the estimation unit 37 calculates the initial carrier frequency fd from the calculated frequency error (Doppler frequency) Derr and the search carrier frequency fs set in the primary search process and the first secondary search process by calculating fd = fs + Derr. (S108).

  If the search range of the second secondary search process obtained from the first secondary search process is less than a preset predetermined chip (less than 1 chip in the present embodiment), the control unit 35 performs the first process described above. Similar to the setting of the center code phase and search range of the secondary search process, the center code phase and search range of the second secondary search process are set (S109: No → S104). That is, the control unit 35 sets the code phase that is the maximum code correlation data in the first secondary search process to the center code phase of the second secondary search process, and also performs the first secondary search process. From the obtained time interval t3, the search range of the second secondary search process is set to (1000 [Hz] × t3 / 1540) [chip].

  Then, as shown in the secondary search in FIG. 4, the control unit 35 repeats such secondary search processing while narrowing the search range until the search range in the next secondary search processing becomes less than a predetermined chip. Execute. Note that the detection threshold for secondary search in each search process is set to be higher as the later search process is performed. By setting the detection threshold value that sequentially increases in this way, the code phase that is the maximum code correlation data, that is, the initial code phase of code tracking can be detected more accurately.

For example, in the example of FIG. 4, the search range for the (n + 1) -th secondary search process in the n-th secondary search process, (1000 [Hz] × t _n−1 / 1540) [ When the [chip] is less than the predetermined chip, the search process is terminated and the capture mode is switched to the tracking mode.

  If the search range of the next secondary search process is less than the predetermined chip, the control unit 35 generates a switching control signal for switching from the acquisition mode to the tracking mode, and gives it to the correlator 31. Further, the control unit 35 gives the initial carrier frequency fd calculated by the estimation unit 37 to the carrier tracking unit 34 at this switching timing (S109: Yes → S110).

  By performing the processing as described above, the search carrier frequency fs and the actual carrier frequency fd can be obtained during the execution of a plurality of continuous search processes, in this embodiment, the primary search process and the first secondary search process. Frequency error (the actually observed Doppler frequency) can be detected. Thereby, it is possible to set the initial carrier frequency taking into account the actual Doppler frequency included in the carrier frequency of the actually received positioning signal and set it in the carrier tracking unit. This enables highly accurate carrier tracking from the initial tracking state. In particular, in the concatenated code carrier tracking loop processing as shown in this embodiment, the carrier frequency information estimated by the carrier tracking unit is used for code tracking, so the Doppler frequency calculation processing of this embodiment is performed. Thus, integrated tracking of the carrier and code can be performed more reliably and accurately.

  Then, such a calculation process of the frequency error (Doppler frequency) Derr becomes more accurate as the time between code phases that becomes the maximum code correlation data in the continuous search process becomes longer as shown in FIG. Therefore, the lower the C / No and the longer the search process, the more accurately the initial carrier frequency can be calculated. That is, even if the reception environment is bad, code tracking and carrier tracking can be executed reliably and with high accuracy. Therefore, as shown in this embodiment, if the results of the primary search process and the first secondary search process that are the initial stages of the capture mode (search process group) are used, it is more than the case where other search processes are combined. The Doppler frequency can be calculated with high accuracy.

  By the way, when the above-described frequency error (Doppler frequency) Derr is calculated, for example, the code phase that becomes the maximum code correlation data becomes close to the last code phase in the search range. It is also possible that this could be shortened. In this case, since the time term t1 is extremely small, the frequency error (Doppler frequency) Derr obtained from the above (Equation 2) may be a very large value. That is, as shown in FIG. 7, there is a possibility that the calculation error of the Doppler frequency becomes large and the resolution is lowered.

  In this case, the control unit 35 sets an initial carrier frequency to be given to the carrier tracking unit 34 based on the following conditions.

  FIG. 5 is a diagram showing the concept of each correction process of the frequency error Derr. FIG. 5A shows a case where the calculated frequency error Derr is outside a predetermined frequency range (± 500 [Hz]). 5 (B) shows a case where the calculated error range of the calculated frequency error Derr is partially outside the predetermined frequency range (± 500 [Hz]). FIG. 5 (C) shows the case of FIG. The state after correction in this case is shown.

(1) First, when the calculated frequency error Derr exceeds the above-described predetermined frequency range (± 500 [Hz] in the present embodiment), which is a range of values that can be theoretically taken (in the case of FIG. 5A).
The control unit 35 can only detect that the frequency error Derr exists. Accordingly, the control unit 35 sets the half value of the maximum value of the set frequency range, for example, +250 [Hz] which is a half value of +500 [Hz] in the present embodiment. This is based on the fact that the frequency error Derr increases as the search process proceeds and always becomes a positive value. By performing such setting, the initial carrier frequency can be set from a more realistic frequency error Derr without using a frequency error Derr that cannot be practically obtained.

(2) Next, when the calculated error range of the calculated frequency error Derr exceeds the predetermined frequency range (± 500 [Hz] in the present embodiment) (in the case of FIG. 5B)
The control unit 35 performs correction based on the calculated frequency error Derr. At this time, the control unit 35 acquires the calculation error range of the frequency error Derr from FIG. 7 based on the time intervals t1 and t2, and the frequency error so that the calculation error range of the frequency error Derr falls within the predetermined frequency range. Correct Derr. For example, as shown in FIG. 5C, in this embodiment, when the upper limit frequency of the calculation error range of the frequency error Derr exceeds +500 [Hz], which is the set upper limit frequency, The frequency error Derr is shifted in the “0” direction so that the upper limit frequency falls within +500 [Hz]. And the control part 35 sets an initial stage carrier frequency from the frequency error Derr after the correction | amendment which carried out the frequency shift in this way. By performing such setting, the initial carrier frequency can be set using the more likely frequency error Derr.

  In the above description, the example in which the Doppler frequency and the initial carrier frequency are set based on the search result of the primary search process and the subsequent first secondary search process has been described. You may make it set a Doppler frequency and an initial stage carrier frequency based on the search result by a search process. Further, the Doppler frequency and the initial carrier frequency may be set based on search results obtained by a plurality of consecutive search processes of three or more times.

  In the above description, it is assumed that the Doppler frequency of the search carrier frequency fs is “0”, but the search carrier frequency fs may include a Doppler frequency that is separately roughly estimated in advance. In this case, the actual Doppler frequency can be estimated and calculated by adding the frequency error Derr shown in the above description to the separately roughly estimated Doppler frequency.

  The frequency error Derr may include a clock error. However, the Doppler frequency can be estimated and calculated by separately estimating the clock error and subtracting it from the frequency error Derr.

11-positioning signal receiving antenna, 12-down converter, 13-demodulation unit, 14-navigation message acquisition unit, 15-positioning unit,
31-correlator, 32-accumulator, 33-code tracking unit, 34-carrier tracking unit, 35-control unit, 36-pseudo-range calculation unit, 37-estimation unit,
330-code NCO, 331-code phase detector, 332-first unit converter, 333-first amplifier, 334-second amplifier, 335-integrator, 336-adder, 337-second unit converter Unit, 341-carrier tracking execution unit, 342-third unit conversion unit, 343-fourth unit conversion unit

Claims (13)

A Doppler frequency estimator for estimating a Doppler frequency of a signal spread by a predetermined code,
A correlator for correlating the spread spectrum signal with a replica code based on the code;
A control unit that causes the correlation unit to execute a search process for calculating a correlation level for each predetermined code phase over a predetermined search range and detecting a code phase having a maximum correlation level in a preset estimation carrier frequency When,
The frequency error of the estimated carrier frequency is calculated based on the amount of code shift between the code phases at the maximum correlation level detected by the two search processes and the detection timing interval of the code phase at the maximum correlation level. An Doppler frequency estimation apparatus comprising: an estimation unit configured to estimate the Doppler frequency. The controller is
A primary search process for performing the search process using the entire code as a search range, and a secondary search process for performing the search process in a search range narrower than the search range of the primary search process are performed on the correlation unit. Run
The estimation unit includes
The Doppler frequency is estimated based on the amount of code shift between the code phases of the maximum correlation level obtained by the primary search process and the secondary search process and the detection timing interval of the code phase at the maximum correlation level. The Doppler frequency estimation apparatus according to claim 1. The controller is
The code phase of the maximum correlation level is obtained by obtaining the correlation level for each code phase in a predetermined search range narrower than the search range of the immediately preceding search process, with the code phase of the maximum correlation level by the immediately preceding search process as the center code phase. A second search process for detecting a plurality of times for the correlation unit,
The estimation unit includes
The code shift amount between the code phases of the maximum correlation level obtained by two search processes out of the primary search process and at least one secondary search process, and the code phase that becomes the maximum correlation level The Doppler frequency estimation apparatus according to claim 2, wherein the Doppler frequency is estimated based on a detection timing interval of the Doppler.   The control unit sets the search range based on a time from a code phase of a maximum correlation level by the immediately preceding search process to a last code phase of the immediately preceding search process during the secondary search process. The Doppler frequency estimation apparatus according to claim 2 or claim 3.   The control unit corrects the calculated Doppler frequency to a value within the frequency range when the Doppler frequency is out of the frequency range corresponding to the search range set in the secondary search process used for calculating the Doppler frequency. The Doppler frequency estimation apparatus according to any one of claims 2 to 4.   When the frequency calculation error range of the Doppler frequency deviates from the frequency range corresponding to the search range set in the secondary search process used for calculating the Doppler frequency, the control unit determines that the frequency calculation error range is the frequency The Doppler frequency estimation apparatus according to claim 2, wherein the Doppler frequency is corrected so as to be within a range.   The Doppler frequency estimation apparatus according to any one of claims 2 to 6, wherein the control unit detects only a code phase having a maximum correlation level equal to or higher than a preset threshold value.   The said control part calculates the said frequency error using the center code phase of the said primary search, and the center code phase of the secondary search immediately after the said primary search. Doppler frequency estimation device. The Doppler frequency estimation apparatus according to claim 1,
The control unit includes a code acquisition mode in which a process for acquiring the code of the positioning signal, which is the spread spectrum signal, is performed in a search process used for estimating the Doppler frequency, and a code for tracking the code of the positioning signal Setting a tracking mode and a carrier tracking mode for tracking the carrier frequency of the positioning signal, and switching from the code acquisition mode to the code tracking mode and the carrier tracking mode based on the code acquisition result in the code acquisition mode, A positioning signal acquisition and tracking device,
The controller is
When the new search range in the code acquisition mode becomes less than a predetermined chip of the code, the code acquisition mode is switched to the code tracking mode and the carrier tracking mode,
In the code tracking mode, code tracking is started using the code phase detected by the search process when switching from the code acquisition mode to the code tracking mode, and in the carrier tracking mode, the code estimated by the estimation unit A positioning signal acquisition and tracking device that sets an initial carrier frequency based on a Doppler frequency and starts tracking the carrier frequency. The positioning signal acquisition and tracking device according to claim 9 is provided,
A demodulator that calculates a pseudorange based on a code phase difference in the code tracking mode and a carrier frequency in the carrier tracking mode;
A navigation message acquisition unit for acquiring a navigation message from the positioning signal demodulated by the demodulation unit;
A positioning device comprising: a positioning unit that performs a positioning calculation using the pseudo distance and the navigation message. A Doppler frequency estimation method for estimating a Doppler frequency of a signal spread by a predetermined code,
A code phase that obtains a maximum correlation level by calculating a correlation level between the spread spectrum signal and a replica code based on the code for each predetermined code phase over a predetermined search range at a preset carrier frequency for estimation The search process to detect
The frequency error of the estimated carrier frequency is calculated based on the amount of code shift between the code phases at the maximum correlation level detected by the two search processes and the detection timing interval of the code phase at the maximum correlation level. To estimate the Doppler frequency,
Doppler frequency estimation method. The search process includes a primary search process for performing the search process using the entire code as a search range, and a secondary search process for performing the search process in a search range narrower than the search range of the primary search process. Have
The Doppler frequency is estimated based on the amount of code shift between the code phases of the maximum correlation level obtained by the primary search process and the secondary search process and the detection timing interval of the code phase at the maximum correlation level. The Doppler frequency estimation method according to claim 11. The search process uses the code phase of the maximum correlation level from the immediately preceding search process as the center code phase, acquires the correlation level for each code phase in a predetermined search range narrower than the search range of the immediately preceding search process, and obtains the maximum correlation The secondary search process for detecting a code phase that becomes a level is performed a plurality of times,
The code shift amount between the code phases of the maximum correlation level obtained by two search processes out of the primary search process and at least one secondary search process, and the code phase that becomes the maximum correlation level The Doppler frequency estimation method according to claim 12, wherein the Doppler frequency is estimated based on a detection timing interval of the Doppler.

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